Traditionally, paper media have been used to read documents including advertising or the like. With increasingly enhanced performance of computers and developing Internet technology, opportunities to read documents in electronic media are increasing. Advantages of using paper media include, but are not limited to, large size for legibility, low price, and easiness to grasp several sentences as a whole by quick overview. On the other hand, advantages of using electronic media include, but are not limited to, the following: dynamically changing information and video on the Internet may be displayed, and electronic media are easy to carry around. A new interface is being developed to enhance the potential of documents using electronic media, while taking advantages of the traditional paper media.
The interface above mentioned has functions to acquire an image including a two-dimensional code when the user captures the image of the two-dimensional code on a paper or other display medium in front of him/her using a camera fixed at a certain location or a freely movable camera, and then display additional information related to its document on a display. Recently, an information presentation method using augmented reality (AR) has been proposed as a technology for displaying additional information, which superimposes and displays additional information on a document image or a projected document.
More specifically, the information presentation method using augmented reality is characterized in that additional information corresponding to a two-dimensional code is superimposed and displayed on a display of a camera, camera-mounted PC, or mobile terminal, for example, on the basis of a reference point defined by the four corners and four sides of a captured image of the two-dimensional code and a physical coordinate system based on this reference point. This information presentation method enables the additional information to be related to its display position on a document image and thus enables cooperation between the paper medium and the electronic medium.
FIG. 1A illustrates an example of a document including advertising or the like and a two-dimensional code attached to this document. FIG. 1B illustrates an example of a document image and additional information displayed on a mobile terminal display. As illustrated in FIG. 1A, the two-dimensional code is positioned in a lower right corner of the document, for example, occupying a relatively small area so as not to affect the visibility and appearance of the document. As illustrated in FIG. 1B, a physical coordinate system may be defined as a reference for the two-dimensional code by defining four sides from the four corners of the two-dimensional code and defining a reference point on the basis of their intersections, for example. In addition, a display coordinate system may be defined as a reference for a captured image by defying the upper left corner of the document image displayed on a mobile terminal display as the origin of the display coordinates, for example. Additional information extracted from the modules included in the two-dimensional code is superimposed on the captured image and displayed on the mobile terminal display on the basis of the physical coordinate system and the display coordinate system. Japanese Laid-open Patent Publication No. 2007-257360 discloses a technology that provides a second module outside the two-dimensional code to enhance the performance of detection of the modules included in the two-dimensional code.